Prevalence and incidence of generalized pustular psoriasis in Sweden: a population-based register study.

Background: Generalized pustular psoriasis (GPP) is a severe form of pustular psoriasis with generalized eruption of sterile pustules, often along with systemic symptoms. There is a scarcity of population-based estimates of GPP prevalence and incidence.

Objectives: To estimate (i) the prevalence and incidence of GPP in the Swedish general population and (ii) the prevalence of psoriasis vulgaris within the GPP population.

Methods: We identified cases (2004-2015) with one ICD-10 diagnostic code (base case) for GPP within the Swedish National Patient Register, which covers inpatient and outpatient secondary care. Cases were linked to the Swedish Total Population Register, and point prevalence was estimated as on 31 December 2015. In two alternative analyses we changed case definitions to: (i) requiring two visits (strict case 1) and (ii) requiring two visits of which one was within dermatology/internal medicine (strict case 2).

Results: The base case point prevalence of GPP was estimated at 9.1 per 100 000 (women, 11.2; men, 7.0) and the annual prevalence in 2015 was estimated at 1.53 per 100 000. Among the GPP population, 43% also had a psoriasis vulgaris code. The incidence of GPP in 2015 was estimated at 0.82 per 100 000 (women, 0.93; men, 0.74). The criteria used had an impact on prevalence and incidence estimates: prevalence strict case 1 gave 3.8 per 100 000 and incidence strict case 1 gave 0.42 per 100 000.

Conclusions: Results indicate that the estimated GPP population in Sweden is within the range of previous published estimates. However, estimates were sensitive to the GPP case criteria used. The findings enhance demands for studies using validated diagnostic algorithms.